In modern society, a variety of resins is used as materials for living consumer items including a container for a cosmetic product. Particularly, environmental problems on a global scale are taken into account, and recently, attention is paid to the utilization of a biodegradable resin as a material for a living consumer item, which is a resin capable of degrading in a natural environment. Since such a biodegradable resin is finally decomposed into water and carbon dioxide through hydrolysis thereof or by microbes or an enzyme, it is excellent in that no biological concentration or environmental hormone effect is caused and an environment is not contaminated.
However, the gas-barrier property of a resin molded object that is obtained by molding only resin is generally insufficient. Therefore, when liquid or gas is preserved in a resin molded object such as a container for cosmetic, leakage of content in the molded object or quality change of content in the molded object may be caused. Also, the rate of biodegradation of a biodegradable resin is not necessarily large.
Therefore, in order to improve the gas-barrier property of a resin molded object and to keep the rigidity of the molded object of biodegradable resin sufficiently high and enhance the rate of biodegradation thereof, a resin composition in which an organically modified clay mineral obtained by ion-exchanging cations of a clay mineral for organic ions is added to a resin is used for the resin molded object. Herein, in many cases, an organic onium ion is used for the organic ion for ion-exchange in a clay mineral.
For example, a biodegradable resin that contains a swelling layered silicate and a polyester for which the main repeated units are lactic acid is disclosed as a biodegradable polyester resin excellent in the gas-barrier property thereof (see JP-A-2002-338796). Herein, the swelling layered silicate is, for example, a silicate salt treated with an organic onium ion such as a quaternary ammonium ion in which four mutually independent alkyl or alkyleneoxy groups with a carbon number of 1-30 bond to the nitrogen atom thereof.
Also, as a biodegradable resin composition for keeping the rigidity of a biodegradable resin molded object sufficiently high and enhancing the biodegradation rate thereof, a biodegradable resin composition is disclosed which contains a biodegradable resin and a layered clay mineral organized with a organizing agent dispersed in the biodegradable rein, wherein the average particle diameter of the organized layered clay mineral is 1 μm or less (see JP-A-2001-089646). Herein, the organizing agent is an organic onium compound such as an organic ammonium compound containing a primary, secondary, tertiary or quaternary ammonium ion, an organic phosphonium compound, an organic pyridinium compound, and an organic sulfonium compound.
On the other hand, a layered organic silicate is a compound in which a silyl group having an alkyl group bonds to the oxygen atom of a silanol group (≡Si—OH) of a layered silicate, and a porous layered silicate which selectively adsorbs an alcohol is disclosed (see JP-A-2000-128521). In this porous layered silicate, a silyl group having one alkyl group in which the carbon number of the linear portion thereof is 6 through 20 and one or two hydroxyl groups bonds to a layer of the layered silicate.
However, the heat resistance of the resin composition is insufficient in which an organically modified clay obtained by ion-exchanging cations of a clay mineral for organic onium ions is added to a resin. That is, as the resin composition is heated for molding the resin composition, the color of the resin composition changes to yellow independently of the kind of a resin to which an organically modified clay mineral is added.
Also, when the resin to which an organically modified clay mineral is added is a resin such as a polyester-based resin, a polyesteramide-based resin, and a polyestercarbonate-based resin, the organically modified clay mineral obtained by ion-exchanging cations of a clay mineral for organic onium ions accelerates hydrolysis of the resin so as to reduce the rigidity of a molded object that is formed from a resin composition containing the organically modified clay mineral and the resin.
Further, the quality of content contained in the molded object that is formed from a resin composition containing the organically modified clay mineral may be changed (the smell of the content may be changed).